Method of treating mixtures of liquids and solids.



A. E. VANDERCOOK. METHOD or TREATING rvglxTuREs 0F LlQums AND Solms.

APPLICATION FILED APR. I4, |914.

Patented May 18, 1915.

` n; ATTORNEYS.

' UNT' I) STATES PATEN FFIC.

ALBERT E. VANDER-COOK, ALAMEDA, CALIFORNIA, ASSIGNOR TO CALIFORNIA MACVAN CO., OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA.

METHOD 0F TREATING MIXTURES OF LIQUIDS AND SOLIDS.

Specification of Letters Patent.

Patented May is, i915.

Original-application filed March 9, 1914, Serial No. 823,537. Divided and this application led April 14, 1914. Serial N o. 831,758.

T0 all whom it may Concern Be it known that I, ALBERT E. VANDER- Coon, a citizen of the United States, and a resident of the city of Alameda, county of Alameda, and State of California, have invented certain new and useful Improvements in the Method of Treating Mixtures of Liquids and Solids.

The invention relates to a method of treating mixtures of liquids and solids or semi solids such as are encountered in metallurgical and manufacturing operations. The method is particularly useful in treating ore pulps and slimes in metallurgical operations, and I will so describe it herein, but it is to be understood that the invention is not limited to metallurgical operations, but may be employed in other and manufacturing processes in which slimes` pulps or similar mixtures of solids and liquids are encountered.

This application is a division of my prior application Serial Number 823,507, filed in the llnited States Patent Oflice on March 9, 191i. v

The objects of the. invention are many and diversified and I shall attempt only to state briefly a few of these objects.

One of the objects of the invention is to provide a method of filtering or separating;- the' liquid content of a mixture of the nature of a pulp or slime from the solid or semisolid content without. forming` a cake of the unfilterable material.

Another object of the invention is to provide a method of filtering in which the filterinpr medium is kept continuously clean and in its most efficient filtering condition.

Another object of the invention is to provide an improved process of washing the unfilterable material to remove therefrom substantially all of the liquid originally contained b v the mixture.

The invention possesses other objects and advantageous features. some of which, with the foregoing. will be set forth at length in the following description. where I shall outline in full the method of my invention, and that form of apparatus for carrying` out the method which I have selected for illustration in the drawings accompanying and formingI part of the. present specification. The novelty of the invention will be included in the claims succeeding said description, and in View of the fact that this invention is basic in nature, I desire the claims to cover the invention in whatever form it vmay be embodied. From this it is to be understood that I do not limit myself to the showing made by said drawings and description, as I may vary the process and adopt many variations in the apparatus within the scope of my invention as set forth in said claims.

AIn view of the departure from accepted practice in the present invention, and of the vast importance of the .results obtained thereby, it is deemed necessary to a full disclosure and a proper understanding of the Asignificance of the process hereinafter described to premise the description of the process by clearly indicating the nature of the, problems involved.

As I have stated hereinbefore, this invention is applicable to metallurgical and other processes, but since I am more familiar with metallurgical processes than with the other processes, l will describe it in such connection, but the fact that I describe the inven tion in connection with metallurgical opera.- tions is not to be considered as limiting the use thereof to such processes, since I can conceive of its use in many other processes. In the metallurgical field it is particularly advantage-ons in connection with the cya-nid process, for separating the value bearing cyanid solution from the ore pulp or slimes, but may be used in any process in which liquids and solids or semi-solids in the nature of pulps or slimes are to be separated, either to obtain the solids or semisolids or the liquid.

In the eyauid prceess. the ground or pulverized orc or pulp containing the gold, silver and other values is mixed with a cyanid solution which dissolves the gold. silver and other values and then the value bearing solution is separated from the remaining solid :.ud semisolid material. so that the solution may be subjected to further treatment for v the recovery of the values therefrom. The

cyanid bearing.r pulp or slimes. and by this I mean the mixture of the finely ground or pulverized ore with the cyanid solution` has heretofore been agitated or stirred or mixed in one vessel for a sufiicient length of time,

. From this vessel the' massof pulp or slime has been conveyed directly or indirectly to another vessel or container which constitutes a filter, and'in which .the solid or insoluble material is deposited on filtering surfaces and from which the value bearing cyanld solution has been withdrawn for subsequent treatment. In the filtering process as heretofore practically accomplished, in the filtration of slimes the unfilterable material is deposited on the filtering medium in the form of a cake, which builds up on the filtering surface. The liquid is forced through the filtering medium and the cake by means of a difference in pressure on opposite sides of the filtering medium, and this operation may be accomplished in two ways, that is, either by increasing the pressure on the ingress side of the filtering medium or by reducing the Vpressure on the egress side. These 'two methods of operation have produced suction filters and pressure filters, but in so far as the general filtering operation is concerned, the two types of filters operate to filter in the same manner,.that is, by forming a cake of the unfilterable material on the filtering surface. It is evident that the formation of the cake increases the resistance to filtration and reduces the rate at which the liquid may be withdrawn, without producing any advantageous effects in so far as the filtering is concerned. In fact, this law.

of nature is the law upon which filter presses of the present time operate, since otherwise uniformity in thickness of the cake would not be obtainable. The increasing thickness of the cake at any point greatly reduces the rapidity of filtration at that point, so that the cake is built up uniformly. Since the presence of the cake greatly reduces the rapidity of filtration, it is evident that the efficiency of cake forming filters must necessarily be very low and since all practical slime filters are cake forming filters, it follows that the method of filtering now in use is capable of' vastimprovement. This improvement I have n'iade by providing a filtering process in which no cake is formed. Further than this, after the cake has been formed, it must be removed from thev filtering medium, after it has been washed, and the proper removal of the cake necessitates generally, the use of a large amount of water, which in regions where water is scarce, is a large item of eX- pense. By my process, since no cake is formed, it is evident that the employment of a large amount of sluicing water is not necessary, thereby providing another feature of advantage over the filtering processes now in general use.

Having stated the present status of the filtering art, prior to my invention, it is be lieved to be advisable to set forth some of the disclosures of the present invention.

This invention disclosesfor the first time a practical method of filtering ore pulp or slimes, or similar masses in which the formation of a cake is obviated and also discloses for the first time a practical process of filter'- ing in which the unfilterable material is not deposited upon the filtering medium during the filtering operation.

According to my invention I prevent the formation of a cake on'the filteringmedium by continually directing a plurality of streams of the material to be filtered against the filtering medium. Thenozzles from which these streams issue are preferably movable over the filtering medium so that the moving streams sweep the entire surface of the filtering medium and remove any deposit therefrom as soon as it is deposited The material which constitutes the streams which are forcibly directed against the filtering medium is withdrawn from the mass of material to be filtered in the filtering vessel and is forced back into the vessel thro-ugh the nozzles.v By preventing the unfiltcrable material from forming in a cake o n the filtering medium, the material ren'iains in the form of a pulp and thereforemay be more readily removed or flowed from the filtering vessel after the filtering and washing operations have been completed. y contains between 30% and 50% of moisture, but by maintaining the material in the form of a pulp, the moisture content may be reduced as low or lower than when a cake is formed.

In the cake forming filter there is a certain thickness of cakebeyond which it is not possible to filter, but in thc present process it is possible to filter when a unich deeper body of the thick unfilterable material is present, thereby rendering the discharge of the unfilterable material less frequent. The process is particularly designed to be'used in connection with ore pulps or slimes which consist of a mixture of finely pulverized ore and liquid, and in the following description and claims I shall refer to the material to be filtered as pulp, it being understood that the word pulp includes slimes and covers anyy material which when filtered without agitation will form a cake on the filtering medium.

In the accompanying drawing I have outlined a simple form of the apparatus for carrying out the process of my invention, but it is to be understood that the apparatus is capable of many variations and modifications, and that the invention is not limited to the apparatus shown, nor to any partieular type of apparatus, and that the process may be carried on without the use of theV particular apparatus shown.

In cake forming filters -the cake In said drawing I have shown one form of apparatus for carrying out my process, parts thereof heilig shown in section.

The apparatus illustrated comprises a cylindrical tank 2 into which the pulp or material to be filtered is charged through the launder 3. Arranged in the bottom of the tank, which bottom is preferably slightly conical, is a filtering surface or medium et through which the liquid is forced. A lowering of pressure on the under side of the filtering medium Il is produced by the vacuum pump 5, which is connected to the tank 2 below the filtering medium, by means of the pipes G and 7. Interposed between the tank 2 and the pump 5 is preferably arranged a sealed tank 8, into which the filtered liquid passes.v The pipe Gis connected to tank 8 at the top so that the tank 8 may fill uith liquid Wit-hout causing it to be carried over to the pump. The liquid or solution tank S is preferably provided with a gage glass 9, which indicates the height of the liquid therein, and with a pressure gage 1Q, Which indicates the condition of vacuum obtaining therein. TWhen the tank 8 becomes full or substantially full, the out.- let 13 is opened, the vacuum therein is released, and the tank empties. The pump 5 need not be operated continuously, but may be operated only until a. suflicient vacuum is produced in the tank 8, after which the valve 14 in the pipe 6 may be closed and the pump stopped.

Means are provided for forcibly directing a plurality of streams of material against the surface of the filtering medium to re move the unfilterable material therefrom as soon as it is deposited, and thereby prevent the formation of a cake on the filtering medium. The means for directing the streams against the filtering medium is preferably rotatable, so that the streams sweep the entire surface of the filtering medium, thereb): intermittently removing the deposited material from any particular portion of the medium. The stream directing means consists preferably of a rotatable structure 15 mounted by means of a suitable bearing 1G upon the centrally depending conductor 1'?. The bearing 16 may be-of the submerged water proof frictionless type or of any suitable construction. The 'rotating structure comprises a plurality of hollow arms 1S, each preti/ led r-:ith a pluralit \r of downrsardlr directed inclined nozzles 19. through which the pulp or liquid is forcibly discharged against the filtering medium. The nozzles are spaced differently onl each arm so that ever;y portion of the filtering surface is insured of a cleaning during the rotation of the structure. The nozzles are also broadened or flattened at their discharge ends so that the pulp is discharged in a broad stream Which sweeps a greater" area of the surface of the medium, than if the streams were not spread. The nozzles are preferably inclined in the same general direction with regard to the arms, so that the reaction of the issuing jets or streams will cause the structure to revolve, thereby obviating the necessity of any separate rotating means. The nozzles on the inner ends of ,the arms are preferably curved so that the streams issuing therefrom sweep that portion of the filtering medium lying below the bearing to prevent the accumulation of unlilterable material at that point. lVhere the word moving is employed in the claims in connection with the streams or jets, it refers to a bodily movement of the streams over the surface of the filtering material.

The liquid or pulp which discharges from the nozzles is drawn from the tank 2 and is forced downward through the conductor 17 by means of the centrifugal pump 21, which is preferably arranged below the level of the filtering medium. By virtue of the down flow of pulp or liquid to the rotatable structure, the pressure of the pulp or liquid being circulated exerts itself downwardly on the hearing, thereby preventing the unseating of the structure, which unseating often occurs when the liquid is introduced upwardly into the agitator. For this reason I ani able to employ a higher pressure on the circulating liquid and thereby produce a comparatively rapid rotation of the structure. The speed of rotation varies to some extent with the length of the arms and with three' foot arms, l have usually operated at a speed of twentyi'ive revolutions per minute. The rotatable structure is usually constructed with four radial arms and the rapid rate with which these arms and their corresponding'nozzles follow each other over the surface of the liltering medium. prevents the deposit of any unfilterable material thereon. The suction .side of the pump 2l is preferably connected to the tank Q at a plurality of levels, by the pipes 22. 23. and Q4, which are provided respectively ivith valves 25,26 and 27 so that the pulp or liquid may be withdrawn from different levels. The loiver pipe 24'is arranged within the lower third of the tank and preferably below the. lever of the unfilterahle material remaining when the filtering operation is completed. pipe 2S provided u'ith a valve 9 is connected to the pump lsuction pipe and is utilized in introdur-ing washing liquid or sluicing water. A cock 1 on the pump suction pipe is employed for admitting air or other gas to the circulating pulp. so that the pulp in the tank 2 may be thoroughij.v aerat-ed or treated. Then the pump 21 is operating and the cock 31 is open, air is drawn into the pump and discharges from the nozzles, whence it bubbles up through the pulp and on account of A the agitation of the pulp and the movement of the nozzles the air 1s thoroughly disseminated in small bubbles throughout the entire Pfllhe bottom of the tank 2 is preferably sloped or inclined toward the ltrate di scharge opening 32, so that the filtrate will readily iow from the tank. The filtering medium may be of any desirable or suitable form, and I do not limit myself to the form shown herein. In such form there is secured to the bottom of the tank adjacent the periphery thereof an angle iron 33 bent into circular form and arranged concentrically with respect to the tank. Resting on the horizontal leg of the angle iron are a plurality of spaced metallic bars 34 arranged parallel to each other and extending across the tank. These bars are provided with supports 30 intermediate their ends'which bear against the bottom of the tank and hold the bars spaced and upright. Arranged on the bars 34 is the filtering medium 4 which may be of any desired construction and which may be secured in place by any desirable means. It is to be understood that this describes one way in which the filtering medium may be supported, andthat I do not limit myself to such construction as others may readily suggest themselves and may be employed without departing from the spirit of my invention.

The unilterable material or pulp may be removed from the tank 2 by sluicing it through the discharge pipe 41 which is provided With a valve 42. The filtered liquid discharges through the pipe 7, which is provided with a valve 43.

The filtering medium usually consists of 4canvas and when the tank is charged with pulp or slimes, and the canvas is new, some of the liquid may percolate through the can.-

vas and this liquid often passes through in a muddy condition. It is not desirable to flow this muddy liquid into the solution tank 8,

and for that reason a branch pipe 45 provided with a valve 46 is arranged on the discharge pipe 7, and a valve 47l arranged below the branch, so that the initial flow of liquid may be diverted and returned to the tank 2. As soon as the canvas becomes thoroughly wetted the liquid passes through clear and is directed to the tank 8.

In treating some slimes, particularly those of a colloidal or gelatinous'nature, a small amount of the slimes may become embedded in the pores of the canvas and retard filtration to some extent. When such a condition is noted, the valve 47 may be closed and air or'water under pressure introduced into the discharge pipe 7, as for instance, through theconductor 45. This causesV a return or backward passage of the air or water through the canvas, releasing the material in taining the cyanid solution has been charged' f into the tank and any necessary operation has been completed, the pump 21 is started, drawing pulp from the tank and 4discharging it through the nozzles 19. These streams of discharging pulp are directed against the filtering medium and besides maintaining the pulp in an agitated condition, sweep the entire' surface of the filtering medium and prevent the settlement of the heavier particles of the ore thereon, thereby maintaining it clean. This recirculation of the pulp and the agitation produced thereby brings the ore particles into recurrent intimate contact with the cyanid solution and accomplishes a rapid solution of the values, which is more efficient since all of the particles of the pulp and particularly the larger and heavier particles are held in suspension. During this operation, the air cock 31 may or may no t be opened, depending upon whether or not it is advisable to aerate the pulp. the cyanid solution has been accomplished toa suitable or proper extent, the valve 43 between the solution tank 8 and the solution outlet of the tank 2 is opened and a lowering of pressure produced below the filtering medium. This lowering of pressuremay be produced by previously exhausting the tank 8 or.by starting the air pump 5, and the the filtering medium and conducted to the tank 8. During the filtering operation the After the solution of the values in liquid content of the pulp is forced through pump 21 is continuously operated and the f below the medium.

At the beginning of the filtering operation, the recirculating pulp is withdrawn from the tank 2 through the pipe 22 and as the level thereof lowers, it is withdrawn through the successively lower pipes, until the desired filtration has been accomplished. lhe pulp may be aerated during the filtering operation by opening the air cock 31 and although the air is projected from the nozzles with the pulp, against the filtering surface, no air is drawn through the filtering medium.

The filtering operation may be carried on in several ways. The tank may be charged with pulp and the filtering operation carried on until the desired amount of filterable material has been removed, leaving the unfilterable material contained in the charge, or pulp may be continuously or intermittently added to the tank during the filtering operation. By means of the present process it is possible to operate with a much deeper layer of unfilterable material than is possible in cake forming filters and for this reason it is possible to add pulp to the tank as the filtering operation is carried on, so that after the filtering operation is completed, a deep mass of unfilterable material is present.

When the filtering operation is completed, the unfilterable material still contains some liquid, which is usually the valuable element, and it is desirable to recover this valuable liquid. This is accomplished by introducing wash water into the tank through the pipe 28. the pump. and the nozzles 1f), and this wash water is intimately mixed withl the pulpy unfilterable material and weakens the strength of the solution remaining therein, so that aft-er the weak solution has been withdrawn, a Very small percentage of the values remain in the unfilterable material. After this operation is completed, the unfilterable material still remains in the consistency of a pulp, and may be readily fiowed or sluiced from the tank. This may be done by opening the discharge outlet and sluicing the pulpy mass out by means of a stream of water or by discharging sluicing water through the nozzles. After the unfilterable material has been removed or discharged, it is advantageous to pass water or air or both in a reverse direction through the canvas to remove therefrom any material which may have become embedded in the pores thereof, before the tank is again charged with pulp or slime.

In carrying out the process, it is evident that the filtering medium must be submerged in or covered by the material to be filtered` which, for convenience, I have designated pulp. By the term submerged I mean that the filtering medium is covered by the pulp, which is usually accomplished by charging the pulp into the tank in which the filtering medium is arranged.

I claim:

l. The process of filtering pulp and the like, which consists in covering a filtering medium with pulp, forcing the liquid being like, which consists in covering a filtering medium with pulp, forcing the liquid being filtered through said medium and discharging a plurality of moving streams of said pulp dlrectly against the filtering medium, whereby the formation of a cake of unfilterable material on said medium is prevented.

3. 'Ihe pro-cess of filtering pulp and thev like, which consists in submerging a filtering medium in a vessel of pulp, forcing the liquid being filtered through said medium, withdrawing a portion of said pulp from said vessel and forcing it in a plurality of streams against the surface of said filtering medium whereby a deposit of unfilterable material on said medium is prevented.

4. The process of preventing the formation of a cake in the filtration of pulp and the like, which consists in sweeping the surface of the filtering medium during filtration with a plurality of streams of pulp directly discharged against said surfaces.

5. The process of preventing the formation of a cake in the filtration of pulp and the like, which consists in directing a plurality of moving streams of said pulp against the filtering surface during the filtering operation.

6. The process of treating pulp and the like, which consists in filtering the pulp and simultaneously recirculating a portion of the pulp and projecting it in a plurality of streams directly against the filtering medium.

7. The process of filtering pulp and the like, which consists in submerging a filtering medium in the pulp, forcing the liquid in said pulp through the filtering medium and Simultaneously withdrawing a portion of the pulp and introducing it in a plurality of moving streams discharged directly against the surface of the filtering medii n, whereby the formation of a cake of terable-nmterial thereon is prevented.

8. rl`he process of filtering pulp and the like which consists in submerging a filtering medium in a vessel of pulp, passing the liquid being filtered through said filtering medium in one direction, sweeping the surface of said medium with a plurality of streams of pulp projected against the surface of the filtering medium and occasionally forcing a fluid in the reverse direction through said filtering medium during such sweeping action.

9. The process of filtering pulp and the` like which consists in covering a filtering medium with the pulp, passing the liquid being filtered through said medium, simul- In testimony whereof I have hereunto set .taneously sweeping the surface of the lmy hand at San Francisco, California, this tering medium 'by a plurality of streams 8th day of April, 1914.

*l lof pulp and occasionally passing a iuid i ALBERT E- VANDERCOOK;

j through the filtering medium in the oppo- In presence ofsite direction while maintaining said sweep- `H. G. PRosT,

ingv action. f P. S. PIDWELL. 

